Respiration

                                     RESPIRATION revision (1)

Glycolysis-

·         Occurs in the cytoplasm of living cells that respire (happens in prokaryotic and eukaryotic cells)

·         Stage 1- Phosphorylation: Glucose is a hexose sugar containing 6C atoms.

1.      One ATP molecule is hydrolysed and the resulting phosphate molecule is attached to the 6C glucose to form glucose 6-phosphate.

2.      Glucose 6-phosphate is then changed to fructose 6-phosphate. Another ATP molecule is hydrolysed and the phosphate molecule released is then attached to fructose 6-phosphate at carbon 1. This results in the formation of fructose-1, 6-biphosphate.

3.      The energy released during the hydrolysis of the ATP molecules is used to change fructose-1, 6-biphosphate to Hexose-1, 6-biphosphate.

·         Stage 2- Splitting of hexose 1, 6-biphosphate

1.      Each molecule of hexose 1, 6-biphosphate is split into 2 molecules of triose phosphate.

·         Stage 3- Oxidation of triose phosphate

This process involves oxidation although it is anaerobic. The triose phosphate molecules are dehydrogenated (enzyme dehydrogenase). The hydrogen molecules removed are picked up by the co-enzyme NAD to form reduced NAD. In glycolysis, two molecules of reduced NAD are produced. Two molecules of ATP are also formed at this stage. This is called substrate-level phosphorylation.

·         Stage 4- Conversion of triose phosphate to pyruvate

             Each triose phosphate molecule is converted into a pyruvate molecule (3-carbon) by four enzyme-catalysed reactions. Another two molecules of ADP is phosphorylated (addition of phosphate group) to form ATP molecules (by substrate-level phosphorylation).

·         Products- Originally, 4 molecules of ATP is made but the net gain is two molecules as two molecules of ATP were used to start the reaction. Two molecules of reduced NAD and two molecules of pyruvate.

The link reaction-

·         Occurs in the matrix of the mitochondria. The pyruvate molecules produced during glycolysis is transported via the inner and outer membranes of the mitochondrial membranes to the matrix.

·         The pyruvate molecules are decarboxylated (pyruvate decarboxylase) and dehydrogenated (pyruvate dehydrogenase)…